The present invention relates to an image-reading apparatus such as an image scanner and the like. In particular, the invention relates to an image-reading apparatus devised to be capable of reliably reading an entire image without bearing a deficiency in the image, even if a paper fed from a paper feeder to an image-reading unit advances obliquely (i.e. paper skews).
Image scanners have been in use for a long while as apparatuses for reading a variety of original paper sheets in large volume for a purpose of, for example, electronic filing. Among those image scanners, certain types that are intended for original paper sheet in a size as small as near to a postcard to about A3-size are generally provided with an automatic paper feeding mechanism (hereinafter simply referred to as xe2x80x9cADFxe2x80x9d) for carrying the original paper sheets to be read, and forwarding them one sheet at a time to an image-reading unit.
The ADF comprises a paper-feeding hopper (hereinafter referred to simply as xe2x80x9chopperxe2x80x9d) for carrying a stack of papers (original paper sheets), and a paper-feeding roller disposed on an upper side of the hopper for picking up and forwarding a paper on an uppermost layer by being in contact with it. As a basic structure of the ADF, it further comprises a separation roller and a retard roller positioned in vicinity of a discharge opening for preventing a multiple feeding of papers. In addition, the hopper is provided with a pair of guides for restraining a position of loaded papers widthwise in order to feed the papers straight. Paper is forwarded toward a conveyor path to the image-reading unit in the same orientation without a skew, when the pair of guides is adjusted of their position according to a size of the paper.
Also, by providing the guides with a positional sensor for producing a signal according to a distance that the guides are moved corresponding to a size of the paper, it can determine in advance the size of paper when a position of the guides is set according to a width of the paper. Hence, the image-reading unit is able to carry out readings according to the size of paper by assigning a scanning module in the image-reading unit with a reading area according to a determined value of the paper size.
Papers sent out from the paper-feeding roller tend to skew, if the papers are arranged in a disorderly manner, or the guides on the hopper are left unfitted with a width of the papers, when a sheaf of the papers is loaded on the hopper. Also, in the case of a sheaf of papers consisting of a variety of different size papers, the guides are set in positions on the hopper according to a paper of the largest size among them. For this reason, papers of smaller size are guided without being in contact with the guides, or with only one of the lateral sides being in contact with one of the guides, thereby resulting in unsteady feeding of the papers. Accordingly, it causes the papers to skew more frequently.
On the other hand, when papers of A4-size are used, for example, a reading area for the A4-size is designated automatically in the image-reading unit by way of setting the guides on the hopper in positions. Therefore, the image reading-unit is able to scan over an entire image on the paper, and the image is input as a standard form of image data into a host-computer without any deficiency in a border area of the paper, if the paper is fed in the normal orientation from the hopper.
If an A4-size paper is fed with a skew, however, a marginal area of the paper lies off the scanning area, since the image-reading unit designates the scanning area corresponding to the A4-size. Hence, the image-reading unit produces an image data partially in defect of the marginal area, and makes a reproduced image defective, because it is unable to match the scan with the entire image on the paper.
Some techniques have been suggested heretofore to cope with a skew paper of this nature that occurs from the hopper to the image-reading unit, in that a sensor is provided along the conveyor path for papers in order to detect a skew, and a processing of image is executed in response to a detection of skew by the sensor. For instance, the apparatus calculates a magnitude of skew of the paper according to a signal from the sensor, and rotates a scanning area of the image-reading unit in proportion to a direction and an angle of the skew paper, so as to match the scanning area with the paper. However, if the apparatus carries out a controlled rotation of the scanning area in this manner every time a paper skews, it slows a speed of reading. Hence, it substantially decreases an efficiency of the image reading process, when a large number of papers needs to be processed.
As described, a partial defect in image data due to a skew paper has been a problem with the image-reading apparatus of the prior art, and countermeasures for it have still been unsatisfactory.
A problem to be solved in this invention is to provide an image-reading apparatus that produces no partial defect in image data that is attributable to a skew paper. The problem is solved with a simple method that is to embrace a portion of image lying off a scanning area due to the skew of paper by expanding the scanning area for reading in advance according to a size of the paper.
The present invention relates to an image-reading apparatus, in which an image-reading unit scans over an image on a paper being fed in, and outputs the image on the paper as an image data, and that a reading area of the image-reading unit is set to be greater than a size of the paper. The image-reading apparatus of this invention then reduces the image read by the image-reading unit into the size of the paper, and outputs the reduced data as an image data.
Since the apparatus of the above-described structure reads an image in an area greater than a size of paper, it is able to pick up the image data in a size of the original paper without causing a deficiency in the image even if the paper skews.